As being easily cast, being efficiently alloyed with other metals, exhibiting high corrosion resistance in air, and having high electrical and thermal conductivities, aluminum has been widely utilized in industry.
In particular, aluminum has been mostly used to reduce the weight of vehicles and to increase fuel efficiency, and has been provided in the form of an aluminum alloy, by mixing aluminum with other metals, because the strength of aluminum itself may not be sufficient as compared to the other metals such as iron.
The aluminum alloy has been manufactured by die-casting, which is a precision casting process in which a molten metal is injected into a mold having a cavity that is mechanically processed at high precision in accordance with the shape of the product to be cast, thus obtaining a cast product having the same shape as that of the cavity.
Meanwhile, the aluminum alloy for die casting has to possess properties suitable for use in a process of filling the cavity of the mold with a high-speed high-pressure molten metal within a short time (for example, within 0.1 to 0.3 sec) to solidify it. In particular, appropriate high-temperature viscosity and latent heat may be required, thereby ensuring flowability suitable for high-pressure casting and mitigating shrinkage defects upon solidification.
Examples of aluminum alloys that have been known for use in die casting include ADC10 alloy that contains an amount of about 8 to 12 wt % of silicon (Si) to thus show properties suitable for the die-casting process and A380 alloy that contains an amount of about 2 to 4 wt % of copper (Cu) to ensure the strength required of structural material even without additional heat treatment.
The ADC10 and A380 alloys also include iron (Fe) in a maximum amount of about 1.3 wt % in order to minimally inhibit seizure and corrosion between the aluminum melt and the mold. Typically, side effects including low elongation due to an excess of Fe acicular structure are minimized through structural fineness using quenching, thus enabling the recycling of the alloy, thereby increasing productivity and work convenience.
The ADC10 and A380 alloys may constitute 90% or greater of all alloys for die casting, because of the many advantages thereof, including their properties and high productivity.
When a die-casting process is commonly applied, no heat treatment has been known to be carried out. Recently, however, many attempts have been made to increase alloy strength using high-vacuum die-casting techniques or heat treatment techniques having a short solution treatment time.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.